This invention relates to hydrostatic pressure sensors and other pressure-responsive devices.
The invention is more particularly concerned with hydrostatic release assemblies.
Hydrostatic release assemblies are used on marine vessels to release life rafts, position indicating radio beacons or the like automatically when the vessels sinks. The release assemblies usually have a pressure-sensing mechanism triggered by pressure at a certain depth of water. The assembly may have a spring-loaded knife blade released by pressure to cut a rope securing the life raft or other item of safety equipment on the vessel. Alternatively, the release may have a catch retaining a bolt, the catch being released at depth to allow withdrawal of the bolt.
The release mechanism usually includes a flexible diaphragm enclosing a sealed chamber, so that, as pressure increases, the diaphragm is pushed into the chamber and this movement is used to trigger the release. In order to prevent atmospheric pressure changes triggering the mechanism, a vent is used to allow a small flow of air into and out of the sealed chamber. In this way, pressure on opposite sides of the diaphragm is gradually equalized but a sudden change in pressure, caused by sinking in water, will still cause deflection of the diaphragm. Also, although air can flow through the vent, it will cause a considerably greater barrier to the flow of water.
Examples of hydrostatic release assemblies are described in WO 91/16233 and EP 0198805.
The hydrostatic release assembly is a critical part of the safety equipment of a vessel. If it releases too readily, the safety equipment may be lost overboard; if it fails to release, the safety equipment will go down with the vessel. The hydrostatic release assembly is often exposed to the environment since the equipment to be released must be located in a position where it can float free of the vessel. As such, the hydrostatic release assembly must be capable of withstanding harsh weather, rough handling and contamination by the various materials used aboard vessels. It is also desirable that the release assembly can be readily removed to enable servicing of the associated equipment and so that the operation of the release assembly can be checked.